I have 2 SQL 2008R2 servers that have been linked together for about 3 months without any issues and for some reason today the link has just stopped working and I can't get it to work again at all. When a scheduled job runs I get the error report below on both servers.

Any help would be greatly appreciated

DIA\administrator. Named Pipes Provider: Could not open a connection to SQL Server [53]. [SQLSTATE 42000] (Error 53) OLE DB provider "SQLNCLI10" for linked server "172.20.20.12" returned message "Login timeout expired". [SQLSTATE 01000] (Error 7412) OLE DB provider "SQLNCLI10" for linked server "172.20.20.12" returned message "A network-related or instance-specific error has occurred while establishing a connection to SQL Server. Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online.". [SQLSTATE 01000] (Error 7412). The step failed.